Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with an n-type window layer (e.g., including cadmium sulfide (CdS), cadmium selenide (CdSe), and the like) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. For example, CdTe has an energy bandgap of about 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap semiconductor materials historically used in solar cell applications (e.g., about 1.1 eV for silicon). Also, CdTe converts radiation energy in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in cloudy conditions as compared to other conventional materials.
The junction of the n-type layer and the p-type absorber layer (i.e., the CdTe layer) is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the n-type window layer form a p-n heterojunction, where the CdTe layer acts as a p-type layer (i.e., an electron accepting layer) and the n-type layer serves as an electron donating layer. Free carrier pairs are created by light energy and then separated by the p-n heterojunction to produce an electrical current.
During the production of such CdTe PV modules, the heterojunction of the p-type absorber layer and the n-type window layer is typically formed by separately depositing different thin films, followed by annealing. For example, the n-type window layer may be deposited via sputtering deposition in a first deposition system, and the p-type absorber layer may be deposited by close spaced sublimation process in a separate system.
However, a need exists for methods and systems for increasing the efficiency of such separate deposition processes, as well as controlling the intermixing between adjacent thin film layers.